We hypothesized that children with OSAS would have blunted ventilatory and arousal responses in responses compared to normal children. To evaluate this, we tested responses to hypercapnia, hypoxia, hyperoxia and combined hypoxia/hypercapnia during sleep in 8 children with OSAS and 6 normal controls. There was no difference in the number of subjects arousing to the metabolic stimuli, the time to arousal or the level of SaO2/PCO2 at which they aroused. Similarly, there were no significant differences in ventilatory responses during sleep between the two groups. Three patients with OSAS were re-evaluated following adenotonsillectomy. Two of these had resolution of their OSAS, associated with a decline in PCO2 at arousal of 6-11 mm Hg, but no other changes. One patient did not improve post-operatively, and had an increase in PCO2 at arousal of 5 mm Hg. We conclude that the overall ventilatory and arousal responses are normal in children with OSAS, indicating that a deficit in overall respiratory drive is not the cause of childhood OSAS. We speculate that other factors must therefore account for the decreased upper airway muscle function occurring during obstructive episodes in children with OSAS.